JP2013535143A - Alternative feedback types for downlink multi-user MIMO configurations - Google Patents

Abstract

A method in a communication network, obtaining a description of a plurality of communication channels each associated with one of a plurality of receivers, and a plurality of steering vectors provided one for each of the plurality of receivers, Each steering vector corresponding to one of a plurality of receivers via a plurality of antennas and corresponding to one of the plurality of communication channels. Each steering vector is used to communicate data on one of a plurality of communication channels, and each steering vector is transmitted to another communication channel in the corresponding communication channel. Generated to reduce interference caused by simultaneous transmission of data at The law is provided.
[Selection] Figure 2

Description

  The present disclosure relates generally to communication networks, and more particularly to wireless networks that utilize space division multiple access (SDMA).

  This application is based on US Provisional Patent Application No. 61 / 355,480 filed on June 16, 2010, and US Provisional Patent Application No. 61 / 360,361 filed on June 30, 2010. US Provisional Patent Application 61 / 368,480 filed July 28, 2010, US Provisional Patent Application 61 / 370,633 filed August 4, 2010, 2010 Claims the benefit of US Provisional Patent Application No. 61 / 372,670, filed on Aug. 11, 1999, the entire contents of which are hereby incorporated by reference.

  The background description provided herein is for the purpose of summarizing the context of the present disclosure. The current inventor's achievements of the present application as described in the background art, whether without the implied or explicit recognizable prior art to the present disclosure, as well as the aspects of the description that would not deserve prior art at the time of filing, Please understand that there is no point.

  Wireless local area network (WLAN) technology has made rapid progress over the past decade. The WLAN standards (such as IEEE 802.11a, 802.11b, 802.11g, and 802.11n standards) have improved single user peak data throughput. For example, the IEEE 802.11b standard specifies a single user peak throughput of 11 megabits per second (Mbps), and the IEEE 802.11a and 802.11g standards specify a single user peak throughput of 54 Mbps. In the 802.11n standard, a single user peak throughput of 600 Mbps is specified. With the new standard IEEE 802.11ac operating at 5 GHz, which overlaps with the legacy IEEE 802.11a / n system, there is also an expectation of throughput exceeding 6.9 Gbps. Unlike other standards, the 802.11ac standard allows simultaneous communication from one access point to multiple different client stations.

  A WLAN typically operates in unicast or multicast mode. In unicast mode, an access point (AP) can send information to one user station at a time. In the multicast mode, the same information can be sent simultaneously to the client station group. The IEEE802.11ac standard enables simultaneous transmission to a plurality of client stations in the multicast mode.

  The antenna and associated effective radio channel have high directivity at frequencies of the order of 60 GHz or higher. If multiple antennas are available at the transmitter, receiver, or both, the antenna must be used to better utilize the spatial selectivity of the corresponding radio channel and apply an efficient beam pattern . In general, beamforming involves generating an antenna gain pattern at the receiving antenna that has one or more high gain lobes or beams (as compared to the gain obtained with an omnidirectional antenna), in the other direction. A single processing technique for utilizing multiple transmit antennas to produce an output that is structurally combined with one or more receive antennas, with low gain. For example, when the gain patterns of a plurality of transmitting antennas are configured to generate a high gain leave in the direction of the receiver, the transmission reliability can be improved as compared to omnidirectional transmission.

  In one embodiment, a method in a communication network, the method comprising obtaining a description of a plurality of communication channels each associated with one of a plurality of receivers, one for each of the plurality of receivers. Generating a plurality of steering vectors using descriptions of a plurality of communication channels, each steering vector via a plurality of antennas and with a corresponding one of the plurality of communication channels, Used to transmit data simultaneously to a corresponding one of the receivers, each steering vector is used to communicate data on any of a plurality of communication channels, and each steering vector is a corresponding communication channel Reduce interference caused by simultaneous transmission of data on other communication channels Rubeku produced, a method is provided.

  In another embodiment, an apparatus includes a steering vector controller that receives descriptions of a plurality of communication channels from a plurality of receivers, each communication channel being associated with one of the plurality of receivers, A plurality of steering vectors, one for each receiver, are generated, each steering vector corresponding to one of the plurality of receivers via a plurality of antennas and corresponding to one of the plurality of communication channels Each steering vector is used to communicate data on one of a plurality of communication channels, and each steering vector is transmitted to another communication channel in the corresponding communication channel. To reduce interference caused by simultaneous data transmission It is made, an apparatus is provided.

  In another embodiment, a system comprising a transmitter, the transmitter having a plurality of antennas and a steering vector controller, the system further comprising a plurality of receivers, the transmitter and each of the plurality of receivers Are associated with corresponding communication channels to define a plurality of communication channels, and a steering vector controller generates a plurality of steering vectors based on a feedback steering matrix received from each of the plurality of receivers, A system is provided in which steering vectors are utilized to simultaneously transmit multiple data units to multiple receivers over multiple communication channels via multiple antennas.

  In another embodiment, a system comprising a transmitter, the transmitter having a plurality of antennas and a steering vector controller, the system further comprising a plurality of receivers, the transmitter and each of the plurality of receivers Are associated with corresponding communication channels to define a plurality of communication channels, and a steering vector controller generates a plurality of steering vectors based on feedback null steering vectors received from each of the plurality of receivers, Multiple steering vectors are used to transmit multiple data units to multiple receivers simultaneously on multiple communication channels via multiple antennas, each null steering vector corresponding to multiple communication channels You Define a null space projection of things, the system is provided.

  In another embodiment, the system comprises a transmitter, the transmitter having a plurality of antennas and a steering vector controller, the system further comprising a receiver, wherein the transmitter and the receiver are associated with a communication channel. The receiver generates a null steering vector that defines a null space projection of the communication channel and communicates the null steering vector to the transmitter, and the steering vector controller generates a steering matrix from the null steering vector to A matrix is provided that is utilized to communicate data over a communication channel from a transmitter to a receiver.

  In another embodiment, a method in a communication network comprising obtaining from a receiver a null steering vector defining a null spatial projection of a communication channel between a transmitter and a receiver, from a null steering vector, from a transmitter Generating a steering matrix utilized to communicate data over a communication channel to a receiver.

FIG. 2 shows a block diagram of an example wireless local area network in which an access point (AP) utilizes downlink (DL) space division multiple access (SDMA) steering technology in an embodiment of the present disclosure.

FIG. 3 is a block diagram of a DL SDMA controller utilized by an AP that implements the steering technique of the present disclosure in one embodiment.

6 is a flowchart illustrating an example of a method for generating a steering vector used when simultaneously transmitting DL SDMA to a plurality of stations using a feedback steering matrix according to an embodiment.

FIG. 4 is a flow diagram illustrating an example of a method for generating a pair of steering vectors used by two stations operating in SDMA mode using null steering vectors in one embodiment.

FIG. 4 is a flow diagram illustrating an example of a method for generating a pair of steering vectors using a hybrid feedback steering matrix or null steering vector technique in SDMA mode using null steering vectors in one embodiment.

FIG. 3 is a flow diagram illustrating an example method for generating a steering vector for DL SDMA transmission from a null steering vector fed back from a station in one embodiment.

Figure 3 shows geometrically each stage of householder transformation used to convert a null steering vector to a steering matrix for use in DL SDMA transmission to a single station in one embodiment. Figure 3 shows geometrically each stage of householder transformation used to convert a null steering vector to a steering matrix for use in DL SDMA transmission to a single station in one embodiment. Figure 3 shows geometrically each stage of householder transformation used to convert a null steering vector to a steering matrix for use in DL SDMA transmission to a single station in one embodiment. Figure 3 shows geometrically each stage of householder transformation used to convert a null steering vector to a steering matrix for use in DL SDMA transmission to a single station in one embodiment.

  In the embodiments described below, a wireless network device such as an access point (AP) such as a wireless local area network (WLAN) transmits separate independent data streams simultaneously to a plurality of client stations via an antenna array. In order to reduce the interference experienced by the receiving station for transmission from the AP to one or more other stations, each AP transmits a transmit (Tx) beam steering (hereinafter referred to as “steering”) vector to each station. Create for downlink transmission. In one embodiment, the AP creates a Tx steering vector for the target station, a description of the wireless communication channel between the AP and the target station, and at least one other wireless communication channel between the AP and another station. This is done using the description. In another embodiment, the AP uses a description of the radio channel between the AP and multiple stations to create a Tx steering vector for each song. At various places in this description, examples are made using the term beam steering. However, it should be understood that, alternatively, or in some examples, these beam steering techniques can be characterized as beamforming techniques and vice versa.

  Thus, in some embodiments (eg, some explicit beamforming embodiments), the AP may describe several wireless communication channels (hereinafter “channels”) for the AP to transmit data to the corresponding station. (Referred to as “description”). As described below, the AP uses this channel description to generate a Tx steering vector, thereby canceling known interference at each station and interference between the space-time streams at each station, or Minimize. In at least some of these embodiments, the AP creates multiple Tx steering vectors corresponding to different stations simultaneously. That is, the client device can feed back channel estimation (ie, some form of description of channel estimation (including uncompressed / compressed steering vectors, null space vectors, etc.)) to the AP. . The AP receives information from all clients and determines the final steering vector.

  In other examples (eg, some implicit beamforming embodiments), each client sends packet data to the AP, which performs channel estimation for each of the different clients' channels and uses this to finalize A steering vector is determined.

FIG. 1 is a block diagram illustrating an example of a wireless local area network (WLAN) 10 in one embodiment. The AP 14 includes a host processor 15 coupled to the network interface 16. The network interface 16 includes a medium access control (MAC) unit 18 and a physical layer (PHY) unit 20. The PHY unit 20 includes _NT transceivers 21 that are coupled to _NT antennas 24. Although three transceivers 21 and three antennas 24 are shown in FIG. 1 (ie, N _T = 3), other embodiments of AP 14 have different numbers (eg, N _T = 2, 4, 5, 6, 7, 8 etc.) may be included. The PHY unit 20 also includes a downlink (DL) space division multiple access (SDMA) controller 19 that implements one or more of the techniques for creating the steering vectors described herein.

WLAN10 the stations 25-i contains the K-number of the client station 25 comprising _{N i} antennas. Although three client stations 25 are illustrated in FIG. 1 (K = 3), in various scenarios and embodiments, the WLAN 10 may have a different number of client stations 25 (eg, K = 2, 4, 5, 6, etc.). ) May be included. Two or more client stations 25 may be configured to receive corresponding data streams transmitted simultaneously from the AP 14.

Client station 25-1 includes a host processor 26 coupled to network interface 27. The network interface 27 includes a MAC unit 28 and a PHY unit 29. The PHY unit 29 includes N _l transceivers 30, and the N _l transceivers 30 are connected to N _l antennas 34. Although three transceivers 30 and three antennas 34 are shown in FIG. 1 (ie, N ₁ = 3), other embodiments of client stations 25-1 may have different numbers (eg, N ₁ = 1, 2, 4, 5, etc.) transceiver 30 and antenna 34. The PHY unit 27 may include a channel estimation controller 40 that, in some embodiments, implements some of the techniques for creating the steering vectors described herein. The client stations 25-2 and 25-3 have the same or substantially similar structure as the client station 25-1. In one embodiment, each client station 25-2, 25-3 is structured similarly to client station 25-1, but only two transceivers and two antennas (ie, N ₂ = N ₃ = 2). Have. In other embodiments, client stations 25-2 and 25-3 may include different numbers of antennas (eg, 1, 3, 4, 5, 6, 7, 8, etc.). Although there is only one implementation in the IEEE 802.11ac standard, it is believed that an AP can support up to 8 antennas and support simultaneous communication with up to 4 stations.

In the illustrated embodiment, AP 14, the client station 25-1 and 25-2, and 25-3 to simultaneously transmit a plurality of spatial streams, via each client station 25-i is data _{L i} number of spatial streams It may be set to receive on. For example, the client station 25-1 receives data via three spatial streams (L _l = 3). In this example, L ₁ = N ₁ , but a general client station 25-i can use a smaller number of spatial streams than the number of antennas included in the client station 25-i. Furthermore, when using space-time coding, a plurality of spatial streams may be referred to as space-time streams. If the number of space-time streams is below the number of transmission chains, in some embodiments, spatial mapping is utilized.

In one embodiment, the AP 14 is defined on the one hand by an array comprising antennas 24-1, 24-2, 24-3 and on the other hand by an array comprising antennas 34-1, 34-2, 34-3. It communicates with client station 25-1 via a multiple-input multiple-output (MIMO) channel. In this example, a MIMO channel can be described by a 3 × 3 channel matrix Hl, each component of which includes a channel gain parameter of the stream defined by the corresponding transmit and receive antennas, and a pair of antennas Between the channel phases. Similarly, AP is, each matrix _{H 2} and _{H 3} in communication with the client 25-2 and 25-3 via describe MIMO channel. In at least some embodiments, the dimension of the matrix Hi describing the MIMO channel between the AP 14 and the client station 25-i is N _i xN _T.

  In a protocol such as 802.11n that supports transmission of beamforming in arbitrary mode, or a protocol such as 802.11ac that supports simultaneous transmission of beamforming to multiple users, the AP 14 is down-coded by the channel descriptor Hi. The link channel can be steered to the intended receiving station using one or more spatial streams (Li), which improves the signal to noise ratio at the intended station. Beamforming typically requires (at least in part) channel knowledge about the AP, but this channel knowledge can be acquired at the AP by explicit beamforming or implicit beamforming. Explicit beamforming means that the receiving station communicates the channel knowledge obtained from the AP in the form of a sounding packet by a feedback packet. Implicit beamforming means that the station reverses the AP with respect to the AP. The sounding packet is transmitted using the link, and then the steering matrix is determined.

Referring to FIG. 1, to create a steering matrix for each station, the system transmits the symbol to the client station 25- _i as a symbol vector x _i of dimension L _i xl, and the client station 25-i It can be modeled to receive a signal represented as a vector y _i of dimension N _i xl.

数１に示すように、受信した信号は、意図される成分、他のクライアント局用に意図されている信号による干渉成分、および、雑音成分（次元Ｎ_ｉｘｌのベクトルｎ_ｉで表される）を含んでいる。数１はさらに以下のように記述することができる。

ここで、

が成り立つ。 さらに、信号ｙ_１、ｙ_２、…、ｙ_ｋは、「一まとめで（stacked）」、累積受信ベクトルｙを定義することができる。

ここで、

が成り立つ。 Thus, in one embodiment, the communication, AP 14 is applying each steering vector W _i of dimension N _T xL _i in transmitted symbol vector x _i, to be able to transmit a signal over the corresponding channels Hi Can do. Therefore, when the AP 14 simultaneously transmits data to the stations 25-1, 25-2,..., 25-K, a signal received by the client station 25-i is expressed as follows.

As shown in Equation 1, the received signal, the components being intended, the interference component by the signal which is intended for another client station, and, (represented by a vector n _i dimension N _i xl) noise component Is included. Equation 1 can be further described as follows.

here,

Holds. Further, the signals y ₁ , y ₂ ,..., Y _k can be “stacked” to define a cumulative received vector y.

here,

Holds.

In order to increase the overall throughput of the WLAN 10, it is desirable to reduce the interference components of as many stations as possible without attenuating the intended components. To achieve this goal, in another embodiment, the DL SDMA controller 19 creates a cumulative steering matrix W (including individual vectors W _i , W ₂ ,..., W _K ) An optimum configuration is achieved for the entire group of client stations 25 (that is, interference between the AP and each station is reduced based on simultaneous communication with other stations). In another embodiment, DL SDMA controller 19, individually vector W _i (sequentially) will be created, the interference from other stations or reduce, or to cancel. The reduction of interference can be performed for all the receiving stations or only for some of the receiving stations. For example, the DL SDMA controller 19 uses channel information to reduce interference to users with the highest priority, users with a priority above a certain threshold level, or users with their own priority order. Can do. That is, in some embodiments, the amount of interference reduction may be based on how interference reduction is performed. Still further, the interference reduction described here is merely an example of using channel information. The DL SDMA controller 19 can optimize any metric (if appropriate) by using channel information. Furthermore, although the previous example has been about the DL SDMA controller 19, the techniques described can also be implemented in one or more of the client stations 25-i in cooperation with the channel estimation controller 40. .

Referring to FIG. 2, in one embodiment, the SDMA controller 50 performs the processing of the DL SDMA controller 19, but in other embodiments, the processing of the DL SDMA controller 19 and the channel estimation controller 40 may be performed. . That is, the techniques described herein may be implemented in the AP or partially implemented in the AP and client device. When implemented in the AP 14, the SDMA controller 50 receives a plurality of data streams DATA ₁ , DATA ₂ ,..., DATA _K for simultaneous transmission to each client station. In some embodiments, the data stream DATA ₁ , DATA ₂ ,..., DATA _K includes packets, frames, or other data units. The K forward error correction (FEC) and modulation unit 54 complete the data stream DATA _1, DATA _2, ..., processes the DATA _K, transmitted symbol vector _{x i,} x 2, generates a ... _{x K.} Next, the spatial steering unit 64 applies the steering vector W _i to each transmission symbol vector x _i . In one embodiment, adder 66 adds the resulting vectors to produce an aggregate product vector.

In one embodiment, the steering vector controller 60 receives the channel description from the channel estimation unit 62 and creates the steering vectors W _i , W ₂ ,... W _K that are supplied to the spatial steering unit 64. In one embodiment, each channel estimation description includes various stream channel gain parameters defined by the transmit and receive antennas (which may be a complex number). The channel description in some embodiments is represented in the form of a matrix. In some embodiments, the multi-station channel estimation unit 62 performs measurement of one or more parameters related to the physical channel to determine channel state information (CSI), or W _i , W ₂ ,... W _K. Create other metrics used for. The AP 14 acquires the channel description of the downlink channel between the AP 14 and each station 25-1,..., 25-K by acquiring the CSI feedback determined by or provided from each station 25-i. can do. For example, in explicit beamforming, a channel estimation block 62 is implemented in the client station 25-I by the client estimation controller 40, whereby channel estimation information is determined, for example, in response to a sounding packet from the AP. The In some embodiments, the AP sends a different sounding packet to each client device (eg, via a multicast method). In any case, the client device 25-i transmits the channel estimation information determined by itself to the AP 14 (including the steering vector controller 60). With respect to CSI feedback, the AP 14 uses one or more spatial streams L _i to separately sound the downlink channel for each station so that each client can identify itself from the received sounding packet. And quantified versions of the estimated channel can be fed back. In some examples, because channel estimation unit 62 and steering vector controller 60 create steering vectors W _i , W ₂ ,... W _K with explicit beamforming, channel estimation unit 62 generates feedback signals from each station. Upon receipt, the DL SDMA controller 19 is able to properly determine the appropriate steering vector to minimize or reduce the interference of each station. Thus, in a CSI feedback implementation, channel estimation unit 62 receives CSI feedback from all stations.

  For implicit beamforming, a channel estimation unit 62 is implemented in the AP. In one embodiment, each station 25-i sends an uplink sounding packet to the AP 14, which is received at the channel estimation unit 62. In response, the channel estimation unit 62 performs channel estimation and communicates directly with the steering vector controller 60, which determines the steering vector determination for each client device with reduced interference. Thus, in this example implicit beamforming embodiment, the channel estimation unit 62 of the AP 14 does not utilize the feedback signal, but instead selects the downlink channel based on the uplink sounding packet received from the station 25-I. presume.

  If CSI feedback does not involve the determination of the station side steering matrix calculation, the amount of information fed back is generally very large. Thus, although a CSI feedback is more useful in a beamforming protocol such as 802.11n, a MU MIMO protocol (eg, 802) that has eight or more transmit antennas and may simultaneously transmit to four or more receiver stations. .11ac), the throughput of CSI feedback appears to be prohibitively high.

Thus, in some examples, the multi-station channel estimation unit 62 may generate the steering vectors W _i , W ₂ ,... W _K based on feedback information other than CSI feedback. In general, channel estimation unit 62 may implement techniques suitable for creating a channel description, including those currently known to those skilled in the art. However, the following describes other types of feedback information received by the channel estimation unit 62 (including steering matrix feedback, null space feedback, and hybrid feedback schemes).

When utilizing the techniques described herein, the steering vector controller 60 of one embodiment looks at the multi-channel descriptors H _i , H ₂ ,... H _K at the same time, and steering vectors W _i , W _{2 ,.} And attempts to minimize (or at least minimize) each station's interference, particularly interference caused by communications with other stations. The feedback information and channel estimation unit 62 allows the steering vector controller 60 to use any known technique (zero force (ZF) method, minimum mean square error (MMSE) method, leakage current suppression (LS)) to calculate the steering vector. And block nullification (BN) methods) can be implemented. In embodiments where the AP communicates with only one station, the controller 60 may utilize a single user beamforming (SU-BF) method.

With continued reference to FIG. 2, in one embodiment, the output of adder 66 (eg, an aggregate product vector) is provided to an inverse discrete Fourier transform module (eg, an inverse fast Fourier transform (IFFT) module) 72. The IFFT module 72 is coupled to the digital filtering and RF module 74. When subjected to processing by IFFT module 72 and digital filtering and RF module 74, data corresponding to the aggregate product vector will be transmitted via the antenna array. As described above, an efficient set of steering vectors W _i , W ₂ ,... W _K can simultaneously transmit the intended component of the transmission signal to the corresponding receiving station, and at each station. The transmission pattern is such that the interference component can be minimized (eg, reduced to zero or substantially zero).

In some embodiments, the feedback information transmitted from each station to the AP 14 is a feedback steering matrix V _k , which may be transmitted in a compressed format or in an uncompressed manner. After receiving a sounding packet on the downlink channel from the AP 14, the station calculates the full channel estimate in a known manner and uses this to generate a beamforming steering matrix V, for example, at the channel estimation controller 40. _k can be calculated. Unlike 802.11n, MU MIMO protocol (for example in 802.11ac) requires the AP to communicate with each of the other stations simultaneously, so the AP 14 sets the feedback steering matrix V _k to the specific station K It cannot be directly applied as a steering matrix. Therefore, as shown in the example of FIG. 3, when the steering matrix feedback is received from all K stations, the AP 14 posts the steering matrix to be used for each station, so that the multistation (“multiuser” and To avoid or reduce interference).

FIG. 3 shows an example of a method 100 for creating a steering vector for simultaneous transmission of data to two or more stations. The DL SDMA controller 19 or SDMA controller 50 is configured, for example, in some embodiments to implement at least a portion of the method 100, where a portion of the functionality is directed to the client device 25-i. May be implemented by the channel estimation controller 40. In the method 100, each station 25-1... 25-K determines the name feedback steering matrix V ₁ ... V _K and feeds back the name matrix to the AP 14 (more specifically, the channel estimation unit 62) to obtain the steering vector W. _i , W ₂ ... W _K are determined. In this embodiment, since each station feeds back a matrix covering the downlink channel space, this method will be referred to herein as “range feedback”.

  At block 102, the AP 14 transmits sounding packets in different spatial streams to a plurality of different stations. Two examples are shown. First, the AP 14 sends a sounding packet to two stations (K = 2, ie, 25-1 and 25-2), and in the second example, the AP sends a sounding packet to three stations (K = 3, ie 25-1, 25-2, and 25-3). There may be another example in which the AP 14 transmits a sounding packet to an arbitrary number of users (K = 3, 4, etc.).

In some implementations, at block 104, for example, singular value decomposition (SVD) is applied to the received downlink channel to decompose the sounding packets received by each station 25-1, 25-2 (this block). May be implemented, for example, by the channel estimation controller 40). In another example, the processing of the received sounding packet can be processed by a technique other than SVD. Bureau 25-1, seeking feedback steering matrix _{V 1} of the own station 25-3 obtains its feedback steering matrix _{V 2.} In some embodiments, the feedback steering matrix V _K can also be determined from all the spatial streams L _i used to transmit sounding packets on the downstream link. In other embodiments, each station may utilize a subset of the spatial stream L _i to determine its corresponding feedback steering matrix.

The method 100 can be operated in either a compressed or uncompressed configuration. In the uncompressed configuration, the feedback steering matrix is transmitted to the AP 14 without compression, and in the compressed configuration, the matrix is transmitted to the AP 14 in the form of an angle representing a compressed version of the feedback steering matrix. In any case, in block 104, each station 25-1, 25-2, which is an example of two stations, transmits the feedback steering matrix V _i obtained from the brand to the AP 14, and in block 106, the AP 14 A description of the downlink channel is obtained, this block 106 being performed at least in part by the channel estimation unit 62.

局２５−１で受信する信号はｙ_１であり、局２５−２で受信する信号はｙ_２であり、これらは以下のように表される。

In block 108, the AP 14 can determine the steering vectors W _i , W ₂ ,... W _K based on the feedback steering matrix VK received from each station, but the block 108 may be implemented by the steering vector controller 60. . It is an example of two stations 25-1 and 25-2 is, in the embodiment to provide a feedback steering matrix V1 and _{V 2,} respectively, at block 108, a steering matrix is determined as follows. Computer channel matrix HK for each station, the following relationship between the feedback steering matrix V _K.

Signal received by the station 25-1 is _{y 1,} the signal received by the station 25-2 is _{y 2,} it is expressed as follows.

In order to completely eliminate both users' interference, the AP 14 determines a steering matrix that simultaneously satisfies V ^T ₁ W ₂ = 0 and V ^T ₂ W ₁ = 0. That, AP 14, by selecting the columns that exist in the null space of V1 and V _2, eliminating the interference of each user (null). For example, W ₁ exists in the null space of V ₂ and vice versa.

従って、ＡＰ１４は、Ｖ^Ｔ _１［Ｗ_２Ｗ_３］＝０、Ｖ^Ｔ _２［Ｗ_１Ｗ_３］＝０、Ｖ^Ｔ _２［Ｗ_１Ｗ_２］＝０を同時に満たすステアリングマトリックスを決定することができる。 In another implementation where three stations 25-1, 25-2, and 25-3 provide feedback steering matrices V ₁ , V ₂ , and V ₃ respectively, block 108 steers using the following equation: A matrix can be determined.

Therefore, the AP 14 may determine a steering matrix that satisfies V ^T ₁ [W ₂ W ₃ ] = 0, V ^T ₂ [W ₁ W ₃ ] = 0, and V ^T ₂ [W ₁ W ₂ ] = 0 simultaneously. it can.

  The optimization metric applied at block 108 is interference nulling at each station. However, the AP 14 can utilize any suitable optimization depending on multiple received feedback steering matrices. In some examples, the AP 14 can utilize more complex decision metrics (eg, maximize the total capacity of each receiver or minimize the mean square error (MSE) at each receiver). To select a steering vector to be used). Other decision metrics include zero force, leakage current suppression, and the like. In some embodiments, steering vector controller 60 performs at least a portion of block 108.

In block 108, the steering vectors W _i , W ₂ ,... W _K for each station are simultaneously generated in consideration of the multi-channel description obtained in block 106. In one scenario, three steering vectors for use at three receiving stations are generated simultaneously taking into account three channel descriptions corresponding to the three channels for simultaneous transmission of data to each station.

  In method 100, each station feeds back to AP 14 the entire vector set of corresponding steering matrices (ie ranging feedback). In other embodiments, instead of feeding back the entire steering matrix, the station may provide a null steering vector that covers the null space of the corresponding steering matrix VK (specifically, a null space feedback formed from a set of vectors in the steering matrix V). It is also possible to feed back a set of vectors that are signals). FIG. 4 describes an example of a method 300.

  FIG. 4 is a flow diagram illustrating an example of an AP-implemented method 200 for generating a pair of transmit steering vectors for simultaneous transmission of data to a corresponding pair of stations in one embodiment. In method 200, a steering vector is generated that forms an aggregate steering vector similar to, for example, a block-nullified aggregate steering vector. In some embodiments, the DL SDMA controller 19 or SDMA controller 50 is configured to implement the method 200.

At block 202, information (eg, a mathematical description) of a first null steering vector of a communication channel between the AP and the first station is received. The first null steering vector corresponds to the null space projection of the first communication channel. In other words, in the communication channel described is H _1, the first null-steering vector, AP 14 is the complete signal station H ₁ is via a communication channel describing receives or substantially to completely attenuated, It is a vector that can be used by AP14. In this way, the AP 14 can prevent the first station from interfering in communication with the second station by using the null space steering vector of the first station. At block 204, information of a second null steering vector of a communication channel between the AP and the second station is received. Similar to the first null steering vector, the second null steering vector is used by AP 14 to fully or nearly completely attenuate the signal received by the station via the communication channel described by H _2. A vector that can be used. Although blocks 202 and 204 are each shown separately, they can be performed simultaneously and can be performed at least partially using channel estimation unit 62.

In blocks 206 and 208, a steering vector utilized in simultaneous downlink transmissions for the first station and the second station is generated utilizing the first null steering vector and the second null steering vector. In particular, the channel described by H ₁ and the steering vector W ₁ used in the first station are assigned the value of the second null steering vector, and the steering vector W used in the channel described by H ₂ and the second station. ₂ is assigned the value of the first null steering vector. Thus, as there is no interference from other stations, the pair transmit steering vectors W ₁ and W ₂ are created for the transmission data simultaneously for the first station and second station.

The station can use any number of techniques to determine a null steering vector that is fed back to the AP 14. In one embodiment, each station computes the SVD of the channel matrix (SVD (H _i )) to numerically determine the null space and select an eigenvector having an eigenvalue below a threshold that is implementation dependent. be able to. The collected set of vectors forms the basis for the null space of the channel matrix. In other examples (eg, for implicit beamforming), this same process can be performed at the AP in response to CSI feedback from each client.

Another method for determining the null space is linear projection. For example, if V is assumed to be a column-wise orthonormal matrix such as a singular vector of a channel matrix, V _null = Null (V) = a (I-VV *) W. Is a normalization factor, W is an arbitrary matrix (eg, a column orthonormal matrix) having a number of columns equal to the size of the null space of V, and I may be an identity matrix.

3 and 4 show examples of stations that determine a feedback steering matrix and a feedback null steering vector, respectively. In other embodiments, the station may ask for both. In both range feedback and null space feedback schemes, the amount of feedback depends on the number of transmit antennas at the AP and the number of receive antennas at the client. FIG. 5 shows another feedback scheme 300 that is a hybrid feedback scheme. After the AP transmits the sounding packet at block 302, at block 304, each station calculates the feedback amount in the feedback scheme described above. That is, at block 304, each station determines a complete feedback steering matrix _VK and a null steering vector. At block 306, the station determines which of the two feedback signals has the smallest amount (which of the two feedback signals result in the least amount of size on the feedback signal). The station feeds back a corresponding feedback signal to the AP 14 and the type of feedback sent from this client to the AP may be indicated in the category field of the management action frame in some embodiments. Depending on the type of signal fed back, either method 100 or 200 may be implemented, and at block 310, the AP may determine a steering vector.

  In other embodiments, the AP may request each station to provide a particular type of feedback based on the AP's own estimate of the amount of feedback expected to be required for each type of feedback. it can.

  The type of feedback from the station (ie CSI, uncompressed beamforming, compressed beamforming, or null space vector) is 3 bits high throughput (HT) control field or very high throughput (VHT) in the MAC header of the feedback frame It may be specified as a steering subfield field of the control field.

  In all of the previously described feedback methods 100, 200, 300 (e.g., feedback steering matrix, null steering vector, or a hybrid that is a compromise of these), each station is optionally (or forced) to space in the feedback frame. A stream (Nss) number subfield can be attached, and this value Nss specifies the number of spatial streams to be used when the AP communicates with a specific station. The AP uses a specified number of spatial streams or a smaller number of spatial streams depending on conditions determined on the AP side (description of feedback channel from each station and interference avoidance determined by the AP). be able to. Each station can determine the number of spatial streams (Nss) suitable for it.

  In some examples where a station transmits a feedback steering matrix, the number of streams (Nss) is less than or equal to the number of columns (Nc) in the singular vector feedback matrix. In some examples of null steering vector feedback, the number of spatial streams (Nss) is less than or equal to (Nrx−Nnull), Nnull is the number of columns in the feedback, and Nrx is the number of antennas in the station. For example, in the case of a station having three antennas (for example, 25-1), it is possible to select to indicate two streams in its own multi-station packet (Nss = 2) and to use a spare receiving antenna for interference reduction It can be so.

  In some embodiments, the station is further (or forced) to add a signal-to-noise ratio (SNR) averaged value in the received downlink channel (ie, tone) to the feedback signal stream. Can do. The number of SNRs used to determine the linear average may be Nc or (Nrx-Nnull) or less. In this way, for null steering vector feedback, the number of SNRs transmitted back to the AP implies the number of streams (Nss) desired at the transmitting station.

  In some embodiments, the number of spatial streams shown (Nss) shares the same feedback steering matrix V format for multiple user (multi-station) feedback (eg 802.11ac) and single user (ie one station) feedback Can be expanded. For example, the station can always feed back the V matrix with the highest possible channel rank (or the largest number of singular vectors).

  In some embodiments, instead of providing an Nss field, each station may include a desired number of space-time streams Nsts in the feedback frame. For example, a station may provide an Nsts field for single user communication as described below and / or for multiple user communication as described above. A space-time stream is a stream of modulation symbols formed by applying a combination of spatial and temporal processing to one or more spatial streams of modulation symbols. The feedback frame includes both subfields, and if the feedback steering matrix V is used for single user beamforming, it indicates the number of columns in the preferred Nsts or V, and the feedback steering matrix V is multi-user When used for precoding, the preferred number of columns of Nsts or V is shown.

ここでａは正規化係数であり、Ｗは、ステアリング送信の所望のストリーム数に等しい列数を持つ任意のマトリックス（列正規直交行列）であり、Ｉは恒等行列であってよい。ＡＰは、決定されたＶ'を、シングルユーザステアリングマトリックスＷ_Ｋとして利用する。 The example method 200 of FIG. 3 illustrates null space vector feedback utilized by the AP to determine steering vectors W _i , W ₂ ,... W _K for simultaneous multi-station beamforming. However, in some examples, the null space vector may be used for single station beamforming where the AP does not communicate with other stations simultaneously. In this example, the AP uses the null space feedback Null (V) to calculate a steering matrix V ′ and uses this matrix to steer to a particular station. The AP can use a number of different methods to determine V ′. In some examples, the AP converts the received null steering vector directly into a range vector. If V _null = Null (V) is a fed back vector, it means that the vector is column orthonormal and the AP determines the ranging vector V ′ based on:

Here, a is a normalization coefficient, W is an arbitrary matrix (column orthonormal matrix) having a number of columns equal to the desired number of streams for steering transmission, and I may be an identity matrix. The AP uses the determined V ′ as the single user steering matrix W _K.

The null space transform may be implemented at the station or at the AP. For example, the station may convert the received range vector into a null steering vector and feed back to the AP. When the AP receives the null steering vector, it converts it to a range vector. In another example embodiment, when the AP receives the feedback steering vector V, the AP creates a null steering vector. That is, in Equation 7, when V _null is a ranging steering vector and not a null steering vector, V ′ in this equation becomes a null steering vector of the ranging vector V _null .

  FIG. 6 is a method 400 that is another technique for performing a null space conversion from a null steering vector to a ranging steering vector to generate a steering vector for single station communication between an AP and one of the stations. Indicates. Although a number of transformation methods can be used, the method 400 employs a householder transformation, at least a portion of which can be performed by the DL SDMA controller 19. Although the illustrated example is described assuming single station communication, in other embodiments, this method can be used for simultaneous communication involving various stations and potentially low interference for each communication channel. It can also be used.

に変換するが、これはこの例では、ステアリングマトリックスＶの最初の３つの列、つまり

（４ｘ３）である。ダウンリンク通信では、ＡＰは、決定されたレンジングベクトル

をステアリングベクトルとして利用する。ヌルステアリングベクトルＶ_ｎｕｌｌは、シングルステーション通信では不要である。 In block 402, the AP transmits a downlink channel signal to a station utilizing the channel matrix H. In the example shown, the channel matrix is a 3x4 matrix and has three spatial streams. In block 404, after receiving the downlink channel signal, the station decomposes its channel matrix to obtain its steering matrix V. At block 406, the station extracts a null steering vector V _null , which in this example is the last column of the V matrix 4x1. At block 408, the station compresses the null steering vector V _null and feeds back to the AP. In block 410, the AP expands the feedback null steering vector V _null (4 × 1) from the station to perform householder matrix transformation, and from the null space signal to the range space vector.

Which in this example is the first three columns of the steering matrix V, i.e.

(4 × 3). In downlink communication, the AP determines the determined ranging vector.

Is used as a steering vector. The null steering vector V _null is not necessary for single station communication.

とＶ_ｎｕｌｌとの積が０になるように（つまり、

となるように）、

をＶ_ｎｕｌｌから求める際の、ハウスホルダマトリックスを決定する方法の一例を示しており、ここで

は、

の共役転置形である。 The following, as used in block 410,

And the product of V _null is 0 (that is,

So that)

_Shows an example of how to determine the householder matrix when determining from V _null , where

Is

This is a conjugate transposed form.

マトリックスをヌルステアリングベクトル４ｘ１Ｖ_ｎｕｌｌから求める処理を説明する。 Before describing the generalized method of null steering vector transformation, in method 400, 4 × 3

Processing for obtaining the matrix from the null steering vector 4 × 1V _null will be described.

ここでｅ_１は、ベクトル［１０…０］である。次にベクトルｖを、以下に従って正規化する。

正規化されたベクトルｖから、ＡＰはハウスホールド反映マトリックスＨＲを以下に従って求める。

ここでＩは恒等行列であり、ＭＴはＡＰの送信アンテナ数である。ベクトル積ＨＲ'・ｘは、ハウスホルダ反映マトリックスＨＲの第１以外の全てがゼロのエントリであり、４ｘ３マトリックスであれば、２番目から最後の列がベクトルｘに直交している。直交に関しては、対応する局と通信するためにＡＰが適用するステアリングマトリックス

は、以下のようにして求められる。

ここでステアリングマトリックス

は、４ｘ３マトリックスである。 The AP receives the null steering vector V _null and causes the transformation vector v to be defined as follows, with the vector x = V _null .

Here, e ₁ is a vector [10... 0]. The vector v is then normalized according to:

From the normalized vector v, the AP determines the household reflection matrix HR according to:

Here, I is an identity matrix, and MT is the number of AP transmit antennas. The vector product HR ′ · x is an entry in which all but the first of the householder reflection matrix HR are zero entries. In the case of a 4 × 3 matrix, the second to last columns are orthogonal to the vector x. For orthogonal, the steering matrix applied by the AP to communicate with the corresponding station

Is obtained as follows.

Where the steering matrix

Is a 4 × 3 matrix.

を求めるために以下のプロセスを実装することができる。 More generally, at block 410, from any null vector V _null for any mxn matrix, the steering matrix

The following process can be implemented to determine:

以下のように、ｖ_ｋを求めるためにこのベクトルをゼロにする。

次に以下のようにして、ハウスホルダ・リフレクタマトリックスをｖ_ｋから定義する。

このハウスホルダ・リフレクタマトリックスから、マトリックスを以下のようにして求める。

ベクトルＡは、Ａ＝Ｑ_ｋＡとして更新して、ＱはＱ＝Ｑ＊Ｑ_ｋとして更新する。 ステアリングマトリックス

は以下のように設定される。

ＡＰは、

であることを確かめて、全ての

の列が、Ｖ_ｎｕｌｌに直交するようにする。 Vector A may be set to be equal to the received V _null (A = V _null ), where [m, n] = size (A). Next, an identity vector Q of length m is obtained using Q = eye (m). In single station communication, all the minimum values except the last m columns can be obtained using the following formula (that is, k = 1: min (m−1, n)). The vector a _k is defined as follows.

This vector is zeroed to determine v _k as follows:

Next, a householder-reflector matrix is defined from v _{k as} follows.

From this householder-reflector matrix, the matrix is determined as follows.

Vector A is updated as A = Q _k A, and Q is updated as Q = Q * Q _k . Steering matrix

Is set as follows:

AP

Make sure that all

_Are orthogonal to V _null .

7-10 show geometrically the householder transformation of the null steering vector of any vector. The matrix P is an operator obtained as P ² = P, and when P is also a Hermitian, P is an orthogonal projector. As shown in FIG. 7, the vector x can be projected in the direction of span {v} and span {v} _null by using P, as both vectors are shown. Are orthogonal to each other. In general, P satisfies the following conditions.

As shown in FIG. 8, the householder reflector HR (v) is an identity matrix reflecting x in a span {v} of an n−1-dimensional subspace. HR (v) can be obtained from the above description as follows.

は、ｘとｘのハウスホルダ・リフレクタＨＲ（ｖ）・ｘとの間の中間点の値である。ＨＲ（ｖ）・ｘは、マトリックスとベクトルを乗算したものである。従ってｘのヌル空間ベクトルを得るには、リフレクタＨＲ（ｖ）は、（投影）ｘをｅ_１＝［１，０，…，０］の方向にマッピングする必要がある。図８における全てのベクトルは、図９では回転されている。つまり、図９に示すように、ＨＲ（ｖ）の二番目から最後の列がｘに直交している（つまり、ｘのヌル空間にある）ので、以下の数式が得られる。

Is the value of the midpoint between x and the householder / reflector HR (v) · x of x. HR (v) · x is a product of a matrix and a vector. Therefore, in order to obtain a null space vector of x, the reflector HR (v) needs to map (projection) x in the direction of e ₁ = [1, 0,..., 0]. All the vectors in FIG. 8 are rotated in FIG. That is, as shown in FIG. 9, since the second to last column of HR (v) is orthogonal to x (that is, in the null space of x), the following formula is obtained.

である。これに対応して、図１０に示すように、ｘとＨＲ（ｖ）・ｘとの間の中間点は、スパン｛ｖ｝＿ヌルの超平面にある。ベクトルｖは正規化されて、ＨＲ（ｖ）＝Ｉ−２ｖｖ'の導出に利用される。この例では、ＨＲ（ｖ）・ｘをｅ_１にマッピングする。しかし他の例では、ＨＲ（ｖ）・ｘを、−ｅ_１にマッピングして、符号を以下のように変えることもできる。

この結果、ｖ＝ｘ＋符合（ｘ（１））・ノルム（ｘ）・ｅ_１となり、ここで符号（ｘ）＝ｘ／ａｂｓ（ｘ）であり、図１０が、ｖの投影結果を示している。 A suitable v for projecting HR (v) x in the base direction is

It is. Correspondingly, as shown in FIG. 10, the midpoint between x and HR (v) · x is in the hyperplane of span {v} _null. The vector v is normalized and used to derive HR (v) = I−2vv ′. In this example, HR (v) · x is mapped to e ₁ . However, in another example, HR (v) · x can be mapped to -e ₁ and the sign can be changed as follows.

As a result, v = x + sign (x (1)) · norm (x) · e ₁ where sign (x) = x / abs (x), and FIG. 10 shows the projection result of v. Yes.

である。Ｉは、（ｋ−１）×（ｋ−１）の恒等行列であり、ＨＲ（ｖ_ｋ）は（ｎ−ｋ＋１）次元のハウスホルダ・リフレクタである。この結果生じうる数式の一例が以下となる。

ＱＲ分解に必要となる浮動小数点演算数は、

となり、ｎ、ｍは、Ａマトリックスの次元の大きさを表す（つまりＡ∈ｃ^ｍｘｎ）。しかし、１つのベクトルのヌル空間ベクトルを得るには、１つのハウスホルダ変換のみで十分であるので（つまり、ｎ＝１）、これによりＸＲ分解計算数を大幅に低減させることができる。 Use a house holder reflector for QR decomposition. For example, A = QRQ ^* A = R. Q can be decomposed into a series of Qk. Q _n Q _n−1 ... Q ₁ A = R, where

It is. I is an identity matrix of (k−1) × (k−1), and HR (v _k ) is an (n−k + 1) -dimensional householder reflector. An example of a mathematical formula that can result from this is:

The number of floating point operations required for QR decomposition is

Where n and m represent the size of the dimension of the A matrix (ie, Aεc ^mxn ). However, since only one householder transformation is sufficient to obtain a null space vector of one vector (that is, n = 1), this can significantly reduce the number of XR decomposition calculations.

  At least some of the various blocks, processes, and techniques described so far may be implemented by hardware that executes firmware instructions, a processor, a processor that executes software instructions, or any combination thereof. When implemented using a processor that executes software or firmware instructions, the software or firmware instructions are stored on a magnetic disk, optical disk, or other storage medium (RAM or ROM or flash memory, processor, hard disk drive, optical disk drive). , Tape drive, etc.). Similarly, software or firmware instructions can be distributed to a user or system by known or desired distribution methods including, for example, computer readable discs, other transportable computer storage mechanisms, or via communication media. A typical communication medium embodies computer readable instructions, data structures, program modules, or program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example only and not limitation, communication media includes wired media such as a wired network or direct wired connection, and wireless media such as acoustic, radio frequency, infrared and other wireless media. Thus, software or firmware instructions can be provided via a communication channel such as a telephone line, DSL line, cable TV line, fiber optic line, wireless communication channel, Internet, etc. (which provides software via a transportable storage medium; Can be viewed as the same or interchangeable concepts) and distributed to users or systems. Software or firmware instructions may include machine-readable instructions that, when executed by a processor, cause the processor to perform various functions.

  When implemented in hardware, the hardware may include one or more discrete components, integrated circuits, application specific integrated circuits (ASICs).

  Although the invention has been described by way of specific examples, which are exemplary only and not intended to limit the invention, modifications, additions, and additions to the disclosed embodiments can be made without departing from the scope of the invention. It is also possible to perform deletion. For example, even when one or more processes in the above-described method are executed in different orders (or simultaneously), a desired result may be produced.

Claims (38)

A method in a communication network,
Obtaining a description of a plurality of communication channels, each associated with any of a plurality of receivers;
Generating a plurality of steering vectors, one for each of the plurality of receivers, using the description of the plurality of communication channels;
Each steering vector is used to simultaneously transmit data to a corresponding one of the plurality of receivers via a plurality of antennas and by a corresponding one of the plurality of communication channels,
Each steering vector is used to communicate data on any of the plurality of communication channels,
Each steering vector is generated to reduce interference in a corresponding communication channel caused by simultaneous transmission of data on other communication channels. Generating the plurality of steering vectors comprises:
The method of claim 1, comprising simultaneously generating the plurality of steering vectors to minimize interference in each communication channel caused by simultaneous transmission of data on the other communication channel. Each steering vector corresponds to a different spatial stream,
Generating the plurality of steering vectors comprises:
The method of claim 2, further comprising generating the plurality of steering vectors to minimize interference to each spatial stream caused by transmission in each other spatial stream. Obtaining the description of the plurality of communication channels comprises:
Receiving a feedback steering matrix from each of the plurality of receivers;
The method of claim 1, wherein each feedback steering matrix is determined from sounding packets received at each station. Obtaining the description of the plurality of communication channels comprises:
Receiving a null steering vector from each of the plurality of receivers;
The method of claim 1, wherein each null steering vector defines a null space projection of a corresponding one of the plurality of communication channels.   6. Each null steering vector is determined at each station by i) performing a singular value decomposition of the channel matrix of the received sounding packet and ii) determining a generated vector having an eigenvalue less than a threshold. Method.   6. The method of claim 5, wherein each null steering vector is determined at each station by performing a linear projection of a feedback steering matrix in a null space. Decomposing the null steering vector received from each of the plurality of receivers;
6. The method of claim 5, further comprising performing a householder transform on each resolved null steering vector to generate a steering vector for communicating with each of the plurality of receivers over a plurality of communication channels.   The method of claim 1, further comprising determining a feedback steering matrix to determine a null steering vector when each receiver receives a sounding packet.   Each receiver determines i) which of the feedback steering matrix and the null steering vector has lower throughput, and ii) which of the feedback steering matrix and the null steering vector is identified The method of claim 9, further comprising transmitting as a corresponding one of the descriptions of a plurality of communication channels. Obtaining the description of the plurality of communication channels comprises:
Receiving an indicated number of spatial streams from each of the plurality of receivers;
The method of claim 1, comprising: determining a desired number of spatial streams for use in communication with each of the plurality of receivers. Obtaining the description of the plurality of communication channels comprises:
The method of claim 1, comprising receiving channel estimation information from each of the plurality of receivers. A device,
A steering vector controller for receiving descriptions of a plurality of communication channels from a plurality of receivers;
Each communication channel is associated with one of the plurality of receivers, and generates a plurality of steering vectors, one for each of the plurality of receivers;
Each steering vector is used to simultaneously transmit data to a corresponding one of the plurality of receivers via a plurality of antennas and by a corresponding one of the plurality of communication channels,
Each steering vector is used to communicate data on any of the plurality of communication channels,
Each steering vector is generated to reduce interference in a corresponding communication channel caused by simultaneous transmission of data on other communication channels. A spatial mapping unit;
The spatial mapping unit is:
Applying each of the plurality of steering vectors to a symbol vector corresponding to a mapping of data to a plurality of different spatial streams, to generate a plurality of product vectors;
14. The apparatus of claim 13, wherein at least some of the plurality of product vectors are combined to generate a combination vector to be transmitted via the plurality of antennas.   14. The apparatus of claim 13, wherein the steering vector controller generates the plurality of steering vectors simultaneously to minimize interference of each communication channel caused by simultaneous transmission of the data on the other communication channel. Each steering vector corresponds to a different spatial stream,
14. The apparatus of claim 13, wherein the steering vector controller generates the plurality of steering vectors to minimize interference to each spatial stream caused by transmission in each other spatial stream.   14. The steering vector controller according to claim 13, wherein the steering vector controller generates the plurality of steering vectors from feedback steering matrices acquired from the plurality of receivers, and each feedback steering matrix is obtained from a sounding packet received at each station. apparatus.   The steering vector controller generates the plurality of steering vectors from null steering vectors obtained from each of the plurality of receivers, and each null steering vector defines a null space projection of a corresponding one of the plurality of communication channels. The apparatus of claim 13.   19. The steering vector controller according to claim 18, wherein the steering vector controller generates one of the plurality of steering vectors by decomposing one of the received null steering vectors and performing a householder transformation. apparatus.   The apparatus according to claim 13, wherein the steering vector controller generates the plurality of steering vectors from channel estimation information acquired from each of the plurality of receivers. A system,
Multiple antennas,
A transmitter having a steering vector controller and
The system further comprises a plurality of receivers, wherein the transmitter and each of the plurality of receivers are associated with a corresponding communication channel to define a plurality of communication channels;
The steering vector controller generates a plurality of steering vectors based on a feedback steering matrix received from each of the plurality of receivers, and the plurality of steering vectors are transmitted from the plurality of antennas to the plurality of communication channels. A system utilized for transmitting a plurality of data units simultaneously to the plurality of receivers.   The system of claim 21, wherein each of the plurality of communication channels is associated with a corresponding plurality of spatial streams. A system,
Multiple antennas,
A transmitter having a steering vector controller and
The system further comprises a plurality of receivers, wherein the transmitter and each of the plurality of receivers are associated with a corresponding communication channel to define a plurality of communication channels;
The steering vector controller generates a plurality of steering vectors based on feedback / null steering vectors received from the plurality of receivers, and the plurality of steering vectors are transmitted to the plurality of communication channels via the plurality of antennas. And wherein each null steering vector defines a null space projection of a corresponding one of the plurality of communication channels, wherein the null steering vector is utilized to simultaneously transmit a plurality of data units to the plurality of receivers.   24. The system of claim 23, wherein each of the plurality of communication channels is associated with a corresponding plurality of spatial streams.   24. The system of claim 23, wherein the steering vector controller generates the plurality of steering vectors simultaneously to minimize interference of each communication channel caused by simultaneous transmission of data on other communication channels. Each steering vector corresponds to a different spatial stream,
24. The system of claim 23, wherein the steering vector controller generates the plurality of steering vectors simultaneously to minimize interference to each spatial stream caused by transmission in each other spatial stream.   24. The steering vector controller according to claim 23, wherein the steering vector controller generates one of the plurality of steering vectors by decomposing one of the received null steering vectors and performing a householder transform. system.   24. Each of the plurality of receivers determines a null steering vector by performing singular value decomposition of a channel matrix of a sounding packet received from the transmitter and determining a generated vector having an eigenvalue less than a threshold. System.   24. The system of claim 23, wherein each of the plurality of receivers determines a null steering vector by performing a linear projection of a feedback steering matrix in a null space.   24. The system of claim 23, wherein each of the plurality of receivers i) receives a sounding packet from the transmitter and ii) determines a feedback steering matrix and a null steering vector.   Each of the plurality of receivers further determines i) which of the feedback steering matrix and the null steering vector has lower throughput, and ii) is identified of the feedback steering matrix and the null steering vector. 32. The system of claim 30, wherein the method is transmitted to the transmitter.   24. The system of claim 23, wherein each of the plurality of receivers transmits an indicated number of spatial streams to the transmitter to identify a desired number of spatial streams for use in communication with each receiver. A system,
Multiple antennas,
A transmitter having a steering vector controller and
The system further comprises a receiver, wherein the transmitter and the receiver are associated with a communication channel;
The receiver generates a null steering vector defining a null space projection of the communication channel and communicates the null steering vector to the transmitter;
The steering vector controller generates a steering matrix from the null steering vector, and the steering matrix is utilized to communicate data on the communication channel from the transmitter to the receiver. The steering vector controller is

To generate a steering matrix V ′, where a is a normalization factor, V _null is the received null steering vector, I is an identity matrix, and W is a predetermined value of the transmitter. 34. The system of claim 33, wherein the system is a steering matrix.   34. The system of claim 33, wherein the steering vector controller generates the steering matrix by decomposing a null steering vector received from the receiver and performing a Householder transform on the decomposed null steering vector. A method in a communication network,
Obtaining from the receiver a null steering vector defining a null space projection of a communication channel between the transmitter and the receiver;
Generating from the null steering vector a steering matrix utilized to communicate data on the communication channel from the transmitter to the receiver.

Generating the steering matrix V ′ according to
37. The method of claim 36, wherein a is a normalization factor, V _null is the null steering vector, I is an identity matrix, and W is a predetermined steering matrix of the transmitter.   38. The method of claim 36, further comprising generating the steering matrix by decomposing the null steering vector and householder transforming the decomposed null steering vector.

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